In the animal husbandry art it is common to use anesthesia to calm and immobilize animals during surgery or for other reasons. During the duration that the animal is under anesthesia it is highly desirable to monitor critical body functions, such as breathing and body temperature, to insure that the animal is stable and is receiving the proper dosage.
The rate of breathing, and the volume of gas being breathed, are significant factors in analyzing the condition of an animal while under anesthesia, and various devices have been proposed for monitoring breathing cycles, for instance, microphone systems are commonly used to give an indication of animal breathing cycles. Respiratory monitors for animals are shown in U.S. Pat. Nos. 3,817,238 and 4,417,589, and respiratory analyzing apparatus suitable for humans or usable with animals are shown in U.S. Pat. Nos. 2,904,033; 3,530,850; 3,990,435 and 4,522,204.
Known respiratory monitors, while capable of sensing and amplifying breathing sounds, do not give an accurate indication of the depth of breathing, the volume of gas being inhaled, variations in breathing characteristics during inhalation or exhalation, and do not provide the degree of sensitivity which is highly desirable.
It is an object of the invention to provide an animal monitoring system for analyzing animal body functions through the characteristics and variations occurring in the respiratory system.
A further object of the invention is to provide an animal monitoring system associated with the gas being breathed wherein the volume of the breathed gas, the velocity of the gas during the breathing cycle, and the temperature thereof, may all be accurately electronically sensed to permit instantaneous readout and indication.
An additional object of the invention is to provide an animal monitoring system sensing the animal breathing cycle wherein an amplified audio frequency is generated whose amplitude or frequency accurately simulates normal breathing sounds.
Yet a further object of the invention is to provide an animal monitoring system using a thermobead transducer within a breathing tube wherein the transducer generates a known temperature and the rate of heat exchange between the thermobead and the breath gas modifies an electronic signal capable of indicating the rate, intensity and volume of breathing characteristics, and may also be used to indicate body temperature.
In the practice of the invention a breathing tube is utilized through which the animal's breath passes. The tube may be associated with an induction mask or an endotracheal tube. Usually, the breathing tube will be incorporated into an anesthetic loop and a sensing transducer within the breathing tube produces an electronic signal indicating the condition of the gas being breathed.
The transducer comprises a very small self-heated thermobead including an electronic circuit which maintains the thermobead at approximately 200 degrees Centigrade. The thermobead is located within the breathing passage tube in direct exposure to the gas being breathed by the animal, and as the gas passes over the thermobead, heat exchange takes place tending to cool the bead and thereby modify the electric conducting characteristics of the thermobead. This varying signal is electronically analyzed and amplified for readout indicating and alarm purposes. The resultant signal can be used to generate an amplified audio output and frequency indicating to the veterinarian the exact condition of the breathing cycle. Another thermobead may also be employed to indicate the temperature of the breath, and directly indicate the animal body temperature. The signal operates electronic displays of the digital or analog type, and may also be used to activate alarms when the signal falls below or rises above predetermined limits.
The rate of heat exchange between the thermobead and the gas being breathed is determined by the temperature of the gas and its flow rate. During each cycle of inhalation and exhalation both the gas temperature and its flow rate vary, and the instantaneous variations in the transducer output permit very accurate analyzing and amplification of the breath characteristics. The velocity of breath gas movement can readily be interpolated to indicate the volume of breathing, and likewise, when sensing the temperature of the animal's breath during exhalation the animal's body temperature may be accurately observed.
The animal monitoring system of the invention is relatively economical, requires a minimum of skill on the part of the operator, and is rugged and dependable.